The present invention relates generally to projection type image displays that make an enlarged projection-screen display of an image displayed on a display screen of an image display element, and to projection optical units for the image displays. More particularly, the invention concerns a projection type image display that makes an enlarged projection-screen display of an image displayed on a display screen of an image display element, and to a projection optical unit for the image display.
Projection type image displays that make an enlarged projection-screen display of an image displayed on a display screen of an image display element which uses a reflection or transmission type of liquid-crystal panel or micromirror are needed to be reduced in depth for compactness, as well as to be able to obtain an enlarged image of a sufficient size on the projection screen. Japanese Patent Laid-Open No. 2001-264627, for example, discloses a projection optical unit designed so that in order to realize the above needs, the unit projects an image in enlarged form by oblique projection, that is, by making image light enter a projection screen from an oblique direction.
Also, Japanese Patent Laid-Open No. 2002-350774, for example, discloses using a curved-surface mirror to conduct the oblique projection involved, and achieving optical adjustment by using the optics involved.
The technique described in Japanese Patent Laid-Open No. 2001-264627 includes disposing a free-form surface mirror of negative power, between projection optics and a projection screen, in order to correct the trapezoidal distortion of a projected image due to oblique projection onto the projection screen. This technique also corrects the aberration caused by the difference in projection distance between any two upper and lower portions of the screen by tilting the image display element or moving it in parallel with respect to coaxial projection optics. The aberration correction involved, however, is likely to misalign the screen-projected image in a vertical direction. Thus, a correction mechanism for the misalignment is further required.
In addition, although a method of correcting an image by moving a free-form surface mirror is disclosed in Japanese Patent Laid-Open No. 2002-350774, the foregoing aberration correction is not considered therein.
Furthermore, neither of the above two patent documents contains any considerations concerning increases in the amount of distortion due to the deformation of the free-form surface mirror in connection with changes in ambient environment.